Fescue toxicosis is a condition of livestock associated with grazing tall fescue (Festuca arundinacea Schreb) infected with its fungal endophyte Acremonium coenophialum Morgan-Jones and Gams. Inasmuch as tall fescue is widely adapted and utilized (Bums and Chamblee, 1979) and incidence of endophyte infection within pastures is high (Hill and Stringer, 1985; Shelby and Dalrymple, 1987), fescue toxicosis is a widespread problem and represents a major economic loss to the livestock industry in the United States.
Tall fescue plantings occupy over 35 million acres in the United States and Canada wherein over 90% of this acreage is infected with Acremonium coenophialum (Bacon et al., 1988). Extreme expense and environmental concerns make it impractical, if not impossible to approach the problem of fescue toxicosis by replanting affected acreage with endophyte-free cultivars. Moreover, the endophyte and plant appear to exist in a symbiotic relationship, suggesting potential problems with the long term survival of endophyte-free cultivars.
Signs of fescue toxicosis include lethargy, reduced weight gain, increased respiration, gangrenous lesions on the extremities, and roughened hair coats. Physiologically, affected livestock have reduced serum cholesterol and alkaline phosphatase (Bond et at, 1984; Stuedemann et at, 1985; Lipham et al., 1989), decreased visceral and peripheral blood flow (Gamer et al., 1978), increased D2 receptor affinity in the corpus striatum (Mizinga, 1991), and reduced prolactin secretion (Lipham et al., 1989). Therefore the pathophysiology of fescue toxicosis includes effects on basal metabolism, cardiovascular, central nervous, and endocrine systems.
The toxic compounds of Acremonium coenophialum infected fescue have yet to be conclusively identified (Putnam et al., 1991). Four classes of alkaloids produced by the endophyte/tall fescue association (loline, peramine, clavine, and ergopeptine) are potentially toxic to grazing livestock. The endophyte, a clavicepitaceous organism, produces ergopeptine alkaloids. Eyropeptine alkaloids are lysergic acid derivatives including agroclavine, elymoclavine, ergovaline, ergosine, and ergocornine (Siegel et al., 1991). In addition, plant derived loline alkaloids are produced in response to the fungal endophyte which are presumed to have a regulatory role in limiting endophyte habitat within the plant. These loline alkaloids are also suspected of being involved with the toxicosis syndrome (Bush et al., 1979). The loline alkaloids include the pyrrolizidine bases N-formyl loline, N-acetyl loline, and loline alkaloids (pyrrolizidine alkaloids).
Many attempts have been made to identify the alkaloid components of endophyte infected tall fescue which produce fescue toxicosis without a definitive answer. Although the unsaturated pyrrolizidine alkaloids have hepatotoxic activity (Mattocks, 1971), intraluminal infusion of saturated pyrrolizidine alkaloids found in tall fescue produced no symptoms of fescue toxicosis (Yates, 1973). However, in combination with acetylcholine, saturated pyrollizidine alkaloids are endowed with smooth muscle contracting capabilities which could result in gangrenous conditions (Bruce et al., 1971).
University of Kentucky researchers reported pyrrolizidine alkaloids as the major toxin associated with fescue toxicosis and demonstrated that thiamine treatment partially alleviated symptoms associated with the disease (Doughtery et al., 1991) (See also U.S. Pat. No. 4,755,519).
However, another group has previously shown that dorsal pedal veins contracted in vitro when exposed to various concentrations of purified lysergic acid derivatives but a mixture of pyrrolizidine alkaloids failed to produce contractile responses (Solomons et al., 1989).
Circumstantial evidence exists that the ergopeptine alkaloids are responsible for fescue toxicosis (Testereci et al., 1991). It has been shown that serum prolactin is frequently decreased in cattle grazing endophyte-infected tall fescue (Thompson et al., 1987) and ergot alkaloids are potent inhibitors of prolactin secretion (Goldstein et al., 1980). In addition, administration of metoclopramide, a type D2 receptor antagonist, increased serum prolactin and weight gains, and changed hair coats from classical fescue toxicosis appearances of long, rough and bronzed to black and shiny in Angus steers (Lipham et al., 1989). Metoclopramide, however, has minor cross reactivity with other receptors which does not exclude effects other than type D2 activity. Likewise, in vitro research evaluating the vasoconstrictive effects of alkaloids assumes that ingestion of tall fescue results in their presence in serum (Solomons et al., 1989).
Therefore, as can be appreciated by a review of the literature, the cause of fescue toxicosis remains unresolved. In addition, despite great economic losses, no economically feasible method to prevent or treat fescue toxicosis exists.
The present invention satisfies this long felt need to protect livestock from fescue toxicosis by providing antibodies and compounds for immunization against fescue toxicosis as well as a method of therapy for affected animals.